Understanding Energy Usage Starts at Home

Since Catherine and Max have written blog posts about their home heating, I thought I’d start the year with my own, equally geeky, piece on electricity use at home.

Electricity is probably the least salient thing we consume. When we are buying groceries, gasoline, clothes, or tickets to a ball game, we are aware that we’re making a purchase and aware of what it costs. But most of us don’t know how much electricity we use — or what we are doing to use it — as we move through life turning things on and off, or having them go on and off automatically. If you read this blog regularly then you obviously care about energy use. So, a fine New Year’s resolution would be to get to know your own electricity consumption. To do so, all you need is $20 and less than an hour of your time.

The $20 is to buy a kill-a-watt, a watt meter that will tell you the electricity usage of anything that plugs into an outlet. Just get the economy version. The more expensive ones claim to translate kilowatt-hours to dollars, but they can’t handle complex electricity tariffs like we have in California where price increases with your monthly usage. (Some tool lending libraries also loan them out. Or you can share one among friends.) Once you get your watt meter, start plugging it in to everything that uses a plug.

Do the refrigerator first. That is usually the largest plug load in your house, and often an easy place for efficiency improvement (by either cleaning the coils or, if the frig is old, getting a new one…your local utility is likely to give you a rebate on the purchase). The nice thing about the kill-a-watt is that it will tell you the elapsed time as well as electricity use for things like refrigerators, which cycle on and off. Leave the kill-a-watt there for a week and come back to see how much electricity it has gobbled up.

My Kill-a-Watt measuring energy use of our washing machine (the plug was in a tight space so a short extension cord came in handy).

If you have a DVR, do that next. You may be surprised at how much electricity it uses, in some cases as much as your refrigerator (if the DVR is oldish and the frig is pretty new). We don’t have a DVR, but our high-definition cable box (without DVR) draws 15 watts all the time it’s on. So I keep it on a power strip.

Then do your computers. If you have a desktop/tower computer, notice how much the flow changes when the screen goes to sleep, cutting power use by half or more. Then watch what happens if you put the computer into sleep mode (from which it wakes up much more quickly than a full shutdown). If you use a laptop, you’ll see the same effect, but scaled down by more than 50%, so you can feel virtuous.

But so far we haven’t touched some of the biggest electricity hogs, things that don’t plug in (or the plug isn’t a standard 110v type that the watt meter is built for): furnace fan, air conditioner, stove, hot tub. (Yes, I cannot tell a lie. I have a hot tub…and really enjoy it.) The watt meter won’t help on those, but if you have a new smart meter, you can probably figure these out with the help of a friend. Many of the new smart meters show, among other things, the real-time energy flow through the meter. On the PG&E smart meter that I have, one area of the readout flashes different metrics in sequence. Here’s a picture of my meter when it was showing that my house was using 1.45 kilowatts.

So, standing at the meter, have your friend turn on the A/C or the furnace fan or whatever you’d like to measure. Then, watch the change in the real-time readout. (This isn’t as helpful for things that have uneven power use such as an electric water heater, which, if you have one, is probably the largest single source of your electricity use.) Here’s what I found out:

Washing Machine: 0.12 kWh per load (using the kill-a-watt)

Electric dryer: 5500w (a good reason to use the drying rack, as we do for most things)

A/C: 4700w (hardly ever use it where we live Orinda, so not a big problem)

Hot tub pump: 100w (but it runs all the time…probably worth putting it on a timer)

Hot tub heater: 6000w (we keep it off most of the time…luckily)

We are generally into the third tier on PG&E’s pricing, which means an incremental kilowatt-hour costs 32 cents. So, that extra load of laundry costs about 3 cents in the washer, but running the dryer for 45 minutes costs about $1.32. The dryer is nearly 20 years old, so we’ll have to replace it sometime; might be worth running a gas line and switching to gas, though I favor just using the drying rack more. Heating the hot tub for an hour (which it takes if it hasn’t been used for a few days) costs almost $2. I still don’t know how much gas my furnace uses when it is on for an hour (that’s next on my list), but the electricity is uses costs about 21 cents per hour.

You might be surprised at how expensive it is to use your appliances or, probably just as likely, surprised at how cheap it is. Putting my computer into sleep mode (2w) at night saves about 11 cents a night compared to leaving it on with the screen off. Easy way to save money or hardly worth the hassle? Or worth doing for the environment even if the savings are puny? You can decide for yourself.

Whatever you decide, as an energy researcher, policy maker, industry participant, or just someone interested in energy issues, becoming an informed consumer yourself is an important step towards understanding household energy use more generally. I bet it will change your view of your own energy consumption and of public policy.